Corrosion wastage model for ship crude oil tanks C. Guedes Soares a, * , Y. Garbatov a , A. Zayed a , G. Wang b a Centre for Marine Technology and Engineering (CENTEC), Technical University of Lisbon, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa, Portugal b American Bureau of Shipping, Technology, Operational Safety & Evaluation, ABS Plaza, 16855 Northchase Drive, Houston, TX 77060-6006, United States article info Article history: Received 13 April 2008 Accepted 14 August 2008 Available online 29 August 2008 Keywords: Steel corrosion Marine environment Oil tanker abstract This study investigates the effects of temperature, carbon dioxide and hydrogen sulphide concentrations on the corrosion behaviour of ship steels subjected to crude oil tank atmospheres. A new corrosion wast- age model is proposed based on a standard non-linear time dependent corrosion model modified by the effect of the different environmental factors contained in the crude oil tank atmosphere. The new corro- sion model assesses the corrosion degradation under stationary environmental conditions denoted as ‘‘short-term”. The long-term corrosion degradation is assessed by considering the succession of the var- ious environmental conditions that can be present in the tank and adding the corrosion damage incurred during each of them. Corrosion records depending only on time are used to calibrate the standard model while the effect of environmental factors in increasing or decreasing the corrosion rate is based on for- mulations published by other authors. A numerical example of a representative application of the new corrosion model is presented, to demonstrate how to apply the model. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Crude oil is one of the most important raw materials for the pro- duction of energy and crude oil tankers play a strategic role in its transportation. The risk of oil tanker accidents is particularly high, which has been shown in the last decades by many accidents with enormous mass of oil spillage into the sea. These oil spillage disas- ters endangered the natural life and caused an economical loss due to crude oil loss, ship damage or ship out of service time and due to the expenses necessary to deal with oil pollution. An example is the Prestige accident of November 2002, which spilled more than 35,000 tones, with a similar amount left inside the sunken tanker leading to the pollution of many kilometres of coast in Spain and France. The sinking of the Erika off the coast of France in December 1999 spilled 20,000 tones of oil and polluted 400 km of the French coast. The investigations into the Erika inci- dent carried out by the French government and the Maltese mari- time authority concluded that age, corrosion, insufficient maintenance and inadequate surveys were all strong contributing factors to the structural failure of the ship. Although some of these accidents were caused by human errors, another big part is related to material degradation caused or influenced by undetected corro- sion [1]. Corrosion is considered the most important factor leading to such age-related structural degradation of ships and of other types of steel structures. Corrosion involves the interaction between me- tal or alloy and its surrounding environment, and it is affected by the properties of both the material and the surrounding environ- ment. Corrosion can take different forms of general attack, pitting corrosion, stress corrosion cracking, corrosion fatigue, fretting cor- rosion, filiform corrosion, weld corrosion, bimetallic corrosion and bacterial corrosion. General corrosion, which is a common form of corrosion, is spread over the whole surface of the metal. Corrosion can lead to thickness reduction, and may facilitate fatigue cracks, brittle fracture and unstable failure. The importance of the studies of the crude oil tank corrosion increased considerably in the last few decades, because of the need to predict better the corrosion in oil tankers that have been prone to some spectacular disasters. Crude oil has a complex composition and it varies widely in their physical/chemical properties. The melting point, boiling point, vapour pressure, partition coefficient and water solubility characteristics of crude oils can differ in the oil producing regions as well as within a specific production field. Despite these wide ranging physical and chemical characteristics, some generaliza- tions can be made regarding the characteristics and influence of crude oil on corrosion. While the corrosion rates may vary, the chemicals causing the largest problems are almost universal. CO 2 and H 2 S gases, in combination with water, create most of the cor- rosion problems in crude oil tanks. Other problems include micro- biological activity and the solids accumulation. The corrosion in the ballast tanks is much different from that in the cargo tanks and both of them are different from the corrosion behaviour in the void spaces of the double bottom and double hull, and machinery space. Even inside the same tank, the corrosion through the void space above the liquid level is different from 0010-938X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2008.08.035 * Corresponding author. Tel.: +351 2184179607; fax: +351 218474015. E-mail address: guedess@mar.ist.utl.pt (C. Guedes Soares). Corrosion Science 50 (2008) 3095–3106 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci